Manufacturing boron fluoride



E. 1 BALDEscHwn-:Lr-:R 2,163,232

MANUFACTURING BORON FLUORIDE 5 Filed April 28, 1937 `2 sheets-sheet 1- June 20, 1939.

l f//f/ 111/7110/ June l20, 1939.

E. l.. BALDEscl-lwlEuER MANUFACTURING BORON FLUORIDE :a sheets-sheep 2 DE', arawn RET/cm.

Fil'ed April 28, 1957 (BASED ou 2155/6072) v- Patented June 20, -1939v v UNITED i STATES PATENT OFI-ica MANUFACTURING BonoN FLUonmE -Emue'r..,nalaeschwieier, Cranford, N. J., signor to Standard Oil Development Company, a cor'- poration of Delaware Application Aprilzs, 1937, serial No. 139,502 l y (ci. zszosy f' 'A 5 Claims.

'This invention relates to an improved method of manufacturing 'boron 'fluoride and more' particularly to a dry method of making same.

The chief method used heretofore commercially for manufacturing boron fluoride is the treatf ment of a'mixture of boric oxide and uorspar with sulfuric acid, but this method has the great' According to the present invention, it has been discovered that a dry process involving the/use of boric oxide and calcium fluoride can be made practical by greatlyincreasingthe proportion of boric oxide used s o that a muchlower temperature can be used which can be obtainedprac-u tically and commercially; it is believed that the formation of -low-melting constituents in the residual products left upon liberation of the boron iluoride helps Ato form a liquid mass or slag and thereby facilitates the liberation of 'thmboron fluoride.

Broadly the invention comprises using a ratio of boric oxide to calcium fluoride (B2Os:CaFz) greater than 0.8, or between the approximatelimits of 0.8 and 3.0,l and preferably between he approximate limits of 1.0 and 2.0. By this process, relatively large volumes of boron iiuoride gas Y are obtained at a relatively low cost, particularly inasmuchhas means are provided for'recovering 40 useful constituents, chiefly boric oxide, from the residual slag. Furthermore, the boron v'uoride produced by this process is of a high degree of purity, being'sbstantially free from SiF4,` HBF4..

-and S03, which are impurities normally encountered in the wet or acid process referred to above. The invention may be carried out in any suit able apparatus, such as a vertical stationary furnace (like a blast furnace used for making iron) lwhich may or may`not' have inclined plates in-itl VV as described in conjunction with the accompany- Aing-drawings, or` a slightly inclined horizontal rotary kiln, either of which may -b'e used for con-V tinuousoperation, or any type of' retort which ymay befused for batch operation. The furnace may be freed of oxygen at the start of operations,

- tion of percent yield of boron fluoride and tem`- 15 by blowing with nitrogen orotlierl inert gas or with some impure or dilute boron iluoride.

In the accompanying drawings, Figure 1 shows a cross-section of a vertical stationary furnace j adapted to be used for the continuous production 5 ofl boron fluoride. Figure 2 is a detail-in Vperspective of an lalternative heating arrangement by which the infdividual plates are heated instead of the furnace walls.

Figure 3 is a detail in vertical section of an alternative construction of the bottom of the furnace.

Figure 4 is a graph or chart vshowing the relaperature to the ratio B2O3:CaFz.

Referring to Figure l in the 'accompanying drawings, a mixture of boric oxide and' calcium fluoride (preferably in ilnegranular form' or in powdered form as would be obtained by pulveriz- 20 ing in a ball mill to a fineness of to 90% passing about mesh) is fed into the top of furnace i through a convenient hopperfeeding device 2 so that the mixture will ydescend slowly on suitable inclined plates 3 with provision for dis- '25 charging solid or liquid residues from the bottom of the furnace leither throughthe bottom opening 4 or side tap hole 5, The interior walls of the furnace i and the plates 3 may be made of iron or` steel, or other suitable alloys, although these 30 materials would not be practical at the high temperatures required by the dry process proposed long ago. The liberated boron fluoride gas is with drawn through outlet 6 near the top of the furnace. I'he Jfurnace may be heated either by 35 means of combustion gases passing through a surrounding chamber 1 .(not shown) or it may be 'heated-by suitable electric rheostat elements 8,

' pills or briquets. Also, if desired, means maybe 45 provided. for preheating the raw 'materials by suitable -countercurrent heat exchangers, using the heat fromeither the boron fluoride gas or the liquid or solidv residues or both. .Figure 2 shows an alternative.heatingarrange '50 ment ,wherebyl the individual inclined plates 3 are heated with lsuitable electric resistance heat-- ers on their under surface, thereby! avoiding the necessity of relying on' a radiation of heat from the walls of the furnace4 i to heat the plates. 55

By this arrangementfof Figure 2, the liberated action products in the form of a molten slag are allowed to accumulate in a slag pit I0 during lgas may, if desired, be confined to a smaller space instead of permeating all of the space be'- tween the plates and the furnace walls. l

I iigure 3 shows an alternative construction of the bottom of the furnace whereby liquid reoperation of the process and periodically discharged through the tap hole 5, in a manner similar to that used in'removing the slag from an iron blast furnace.

cleaning out the slag when desired.

The residues obtained from the bottom of the furnace and consisting chiefly of calcium monoborate, CaO.BzO3, or a eutectic mixture'thereof with calcium di-borate, CaO.2B2Oz, and also containing some fluorine, possibly in the form of calcium fluoborate, Ca(IBF4) "2, may be treated with a suitable dilute mineral acid, such as sulfuric acid or hydrochloric acid, for the recovery of ation of the furnace is so adjusted that the mix ture of boric oxide and calcium fluoride is heated for a period of time of approximately 5 to 30 minutes, ordinarily 10 minutes being suillcient if the heating means used is very emcient. In any.

case, the heating should be continued until subst'antally no more boron fluoride is evolved.

Although it is not desired to limit-the inven- .tion to any particular theories as to the mechanlsm of the reactions involved,the following tentative explanations are advanced in order 'to emphasize some of the advantages of the present process over the process previously proposed by Gay-Lussac. Qne of the most important advantages of the present invention is the use of an operating temperature which is feasible commercially, namely, between the approximate limits-of 9001100 C. or perhaps 1200 C., whereas the prior process required a temperature substantially in excess of 1400 C. which is not practical commercially for this type of process. Another 'advantage of the present process is that after all the boron iluoride has been evolved, "the amount of fluorine left in a chemically combined form in the residue is very much less than (substantially less than 1/2 as much as) in the prior method.v This is veryJ important commercially inasmuch as this residual fluorine is apparently combined in such a chemically stable f orm that it cannot practicallyI be recovered. It is believed that the compound formed is calciiun uoborate, having the formula Ca(BF4)n. 0nthe other hand, with the much larger ratio of. BzOazCaFz, used according to the present invention, as compared to the low ratio used in the 'Gay-Lussac process, a residual productl o r slag is'obtained from which itis practical to recover a substantial proportion of the B203 .contained therein; whereas in the residue from the other process,

the proportion o1' B20: present is `so small that The larger lower operi-l ing or manhole Il may be used for draining'or- Commercially the use of av tremendously large amount of relatively value-` less lime and relatively stable and unrecoverable vfluorine compounds must be handled 4that a processl for recovering the small amount of B20: would not be practical. It is believed that the residue from the prior process contains enough lime to form a tri-calcium borate having the formula 3CaO.B2O: and that under those conditions'no calcium borate. CaO.B:O3. could Vbe or would be formed. According to the present invention, it is believed desirable to use a sufficiently high ratio of BzOazCaFc that the slag residue will contain a substantial amount of calcium borate, CaOBzOJ, and if desired, even some calcium di-borate, CaO.2BzOJ.

For the sake of further illustrating the operation of the present invention, theffollowing table of experimental data is given whlchmay be read in connection with the chart shown in Figure 4 of the drawings'.

Ratio BOTPRF l leld Test No.

Percent BF; G. BF; per Mol. Wt (on Cal" lil) G. used)* BIOri-Cl'l 3l. 8 i2. m 59.8 16.10 65. 5 i3. m 09. l 13. l 59. 5 9. 35

I*Calculated upon the theoretical amount obtainable based `on the ratio ZBF.: BCaFz.

From the above table and the accompanying chart in Figure 4, it is apparent that when the molar ratio of BzOaICaFz is increased from 0.57,' as used in the Gay-Lussac process, to substantially 1.0 or above, there is a great increase ln the percentage of BF: obtained (see curve A in Figure 4), as calculated upon the theoretical amount obtainable based on the ratio of, 2BF::3CaFz according to the chemical reaction:

It is also apparent that the yield BF: based on the total weight of boric oxide and calcium fluoride used is also increased until (as shown in curve B in `Figure fi) it reaches a maximumat a BzOznCaFz ratio of 1.0 or 1.2, after which it gradually is reduced with further increases in the ratio of BnOuCaFz. o f

The optimum ratio of .Bz0:';CaF; to be used will lie approximately between theratios indicated by the highest point in curve A and the operation ofthe invention, nor to the specific details which are given merely for the sake 4of illustration, but only by the appended claims comprises heating a mixture of boric oxide and calcium fluoride having a molar ratio of BzOazCaFz 'in between the approximate limits of 0.8 t0 3.0 and heating Said mixture t0 a tem- 4. Process of producing b oron uoride which comperature within the approximate limits of 900 and 1200o C. to evolve a substantial amount of boron fluoride gas.

2. Process according toclaim 1 in which theratio of B2O3:CaF2 is between the approximate vthe approximate limits 1.0 and 2.0 and reacting said molten reaction mixture to evolve asubstantial amount of boron uorde and leaving a non-gaseous residue containing a substantial amount of calcium mono-berate.

prises comminuting boric oxide and calcium ilu oride, mixing same in a molar ratio of BzO3:CaF2

betweenthe approximate limits of 1.0 and 2.0 and heating said mixture to a temperature between the vapproximate limits of 900 and 12004 C. until substantially no more boron iluoride gas is evolved from said mixture.

5. Process of producing boron uoride whichY comprises heating a mixture of boric oxide and calcium uoride in a molar ratio of B2O3:CaFz of labout 1.3 to a temperature-in the range of about 900 to about 1200 C.

MAE L. BALDESCHWIELER. 

